Don't let Microsoft Sentinel end up being "just noisy." 3 tips to keep your operations from becoming a formality

 

"There are too many alerts, no one is looking at them anymore"
"I get more than 100 notifications every day, but almost all of them are false positives."
"I put Sentinel in, but I noticed the incident manually."

SIEM is not a "put it in and it's done".
The quality of the operational design can be both a "usable SIEM" and a "noisy device".

1. Why Sentinel is "noisy"

If you enable all of Sentinel's default rules, you'll get hundreds of alerts per day, depending on your environment.
There are three main causes.

• Rule threshold too low: triggered even by normal operations
• Context is not considered: rules that ignore the characteristics of the business system
• Notify not designed: All alerts fly to everyone

If this continues, reps will fall into "Alert Fatigue" and overlook really dangerous notifications.

2. Three Approaches to Improving Rule Quality

(1) Categorize Rule Priority

The main premise is that not all rules are treated with the same weight.
Analytics Rules in Sentinel can be configured with Severity.

• High: Immediate response required (account takeover, ransomware, etc.)
• Medium: Check during business hours (abnormal login location, etc.)
• Low/Informational: Weekly reviews are sufficient

Simply notify High on-call and Low only accumulate in Log Analytics Workspace, dramatically reducing noise.

(2) Tuning to the Environment

It is dangerous to use the default rules as they are.
For example, the rule "Late-night sign-in detection" will be activated when overseas site access is normal for global companies.

Let's check the following for each rule:

• When to ignite (trigger condition)
• Is it normal or abnormal in your environment?
• Can I set an Exception list?

3. Notification Design: Who, What, and Where to Receive

The destination design for alerts is the operational flow itself.
Common mistakes: "Email all notifications to everyone"

Instead, design it like this:

• High Alerts → Microsoft Teams specific channels + direct mentions to reps + on-call such as PagerDuty
• Medium alerts → Teams notifications only (confirmed the next business day)
• Low alerts → aggregated into weekly reports and emailed

You can use Logic Apps and Playbooks to automate the assignment of recipients based on the content of your alerts.

4. Determine the boundaries of responsibility

If you don't specify who will respond to which alerts and within how many minutes, SIEM is a piece of cake.
Decide in advance who will investigate and who will decide to stop the system after Sentinel raises an alert.

5. Continuous improvement to make it "rotating monitoring"

Just because you've tuned it once, the rules won't be optimal forever.

• As new systems and services are added, new false positive patterns are created
• Change in attack modus operandi reduces detection rule coverage

Create a system to review the "False Positive Rate", "Alert Response Rate", and "SLO Achievement Rate" on a monthly basis.

6. Colorkrew Security's Approach

At Colorkrew Security, we focus on Sentinel's "post-implementation support."

**SIEM is a tool. It is the power of operational design that makes it "rotating monitoring". **
We work together to create a system from rule design, notification design, delimitation of responsibilities, and SLO formulation.